/* inffast.c -- fast decoding
 * Copyright (C) 1995-2004 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "zutil.h"
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"

#ifndef ASMINF

/* Allow machine dependent optimization for post-increment or pre-increment.
   Based on testing to date,
   Pre-increment preferred for:
   - PowerPC G3 (Adler)
   - MIPS R5000 (Randers-Pehrson)
   Post-increment preferred for:
   - none
   No measurable difference:
   - Pentium III (Anderson)
   - M68060 (Nikl)
 */
#ifdef POSTINC
	#define OFF 0
	#define PUP(a) *(a)++
#else
	#define OFF 1
	#define PUP(a) *++(a)
#endif

/*
   Decode literal, length, and distance codes and write out the resulting
   literal and match bytes until either not enough input or output is
   available, an end-of-block is encountered, or a data error is encountered.
   When large enough input and output buffers are supplied to inflate(), for
   example, a 16K input buffer and a 64K output buffer, more than 95% of the
   inflate execution time is spent in this routine.

   Entry assumptions:

        state->mode == LEN
        strm->avail_in >= 6
        strm->avail_out >= 258
        start >= strm->avail_out
        state->bits < 8

   On return, state->mode is one of:

        LEN -- ran out of enough output space or enough available input
        TYPE -- reached end of block code, inflate() to interpret next block
        BAD -- error in block data

   Notes:

    - The maximum input bits used by a length/distance pair is 15 bits for the
      length code, 5 bits for the length extra, 15 bits for the distance code,
      and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
      Therefore if strm->avail_in >= 6, then there is enough input to avoid
      checking for available input while decoding.

    - The maximum bytes that a single length/distance pair can output is 258
      bytes, which is the maximum length that can be coded.  inflate_fast()
      requires strm->avail_out >= 258 for each loop to avoid checking for
      output space.
 */
void inflate_fast(strm, start)
z_streamp strm;
unsigned start;         /* inflate()'s starting value for strm->avail_out */
{
	struct inflate_state FAR* state;
	unsigned char FAR* in;      /* local strm->next_in */
	unsigned char FAR* last;    /* while in < last, enough input available */
	unsigned char FAR* out;     /* local strm->next_out */
	unsigned char FAR* beg;     /* inflate()'s initial strm->next_out */
	unsigned char FAR* end;     /* while out < end, enough space available */
#ifdef INFLATE_STRICT
	unsigned dmax;              /* maximum distance from zlib header */
#endif
	unsigned wsize;             /* window size or zero if not using window */
	unsigned whave;             /* valid bytes in the window */
	unsigned write;             /* window write index */
	unsigned char FAR* window;  /* allocated sliding window, if wsize != 0 */
	unsigned long hold;         /* local strm->hold */
	unsigned bits;              /* local strm->bits */
	code const FAR* lcode;      /* local strm->lencode */
	code const FAR* dcode;      /* local strm->distcode */
	unsigned lmask;             /* mask for first level of length codes */
	unsigned dmask;             /* mask for first level of distance codes */
	code this;                  /* retrieved table entry */
	unsigned op;                /* code bits, operation, extra bits, or */
	/*  window position, window bytes to copy */
	unsigned len;               /* match length, unused bytes */
	unsigned dist;              /* match distance */
	unsigned char FAR* from;    /* where to copy match from */

	/* copy state to local variables */
	state = (struct inflate_state FAR*)strm->state;
	in = strm->next_in - OFF;
	last = in + (strm->avail_in - 5);
	out = strm->next_out - OFF;
	beg = out - (start - strm->avail_out);
	end = out + (strm->avail_out - 257);
#ifdef INFLATE_STRICT
	dmax = state->dmax;
#endif
	wsize = state->wsize;
	whave = state->whave;
	write = state->write;
	window = state->window;
	hold = state->hold;
	bits = state->bits;
	lcode = state->lencode;
	dcode = state->distcode;
	lmask = (1U << state->lenbits) - 1;
	dmask = (1U << state->distbits) - 1;

	/* decode literals and length/distances until end-of-block or not enough
	   input data or output space */
	do {
		if(bits < 15) {
			hold += (unsigned long)(PUP(in)) << bits;
			bits += 8;
			hold += (unsigned long)(PUP(in)) << bits;
			bits += 8;
		}

		this = lcode[hold & lmask];
dolen:
		op = (unsigned)(this.bits);
		hold >>= op;
		bits -= op;
		op = (unsigned)(this.op);

		if(op == 0) {                           /* literal */
			Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
			         "inflate:         literal '%c'\n" :
			         "inflate:         literal 0x%02x\n", this.val));
			PUP(out) = (unsigned char)(this.val);
		} else if(op & 16) {                    /* length base */
			len = (unsigned)(this.val);
			op &= 15;                           /* number of extra bits */

			if(op) {
				if(bits < op) {
					hold += (unsigned long)(PUP(in)) << bits;
					bits += 8;
				}

				len += (unsigned)hold & ((1U << op) - 1);
				hold >>= op;
				bits -= op;
			}

			Tracevv((stderr, "inflate:         length %u\n", len));

			if(bits < 15) {
				hold += (unsigned long)(PUP(in)) << bits;
				bits += 8;
				hold += (unsigned long)(PUP(in)) << bits;
				bits += 8;
			}

			this = dcode[hold & dmask];
dodist:
			op = (unsigned)(this.bits);
			hold >>= op;
			bits -= op;
			op = (unsigned)(this.op);

			if(op & 16) {                       /* distance base */
				dist = (unsigned)(this.val);
				op &= 15;                       /* number of extra bits */

				if(bits < op) {
					hold += (unsigned long)(PUP(in)) << bits;
					bits += 8;

					if(bits < op) {
						hold += (unsigned long)(PUP(in)) << bits;
						bits += 8;
					}
				}

				dist += (unsigned)hold & ((1U << op) - 1);
#ifdef INFLATE_STRICT

				if(dist > dmax) {
					strm->msg = (char*)"invalid distance too far back";
					state->mode = BAD;
					break;
				}

#endif
				hold >>= op;
				bits -= op;
				Tracevv((stderr, "inflate:         distance %u\n", dist));
				op = (unsigned)(out - beg);     /* max distance in output */

				if(dist > op) {                 /* see if copy from window */
					op = dist - op;             /* distance back in window */

					if(op > whave) {
						strm->msg = (char*)"invalid distance too far back";
						state->mode = BAD;
						break;
					}

					from = window - OFF;

					if(write == 0) {            /* very common case */
						from += wsize - op;

						if(op < len) {          /* some from window */
							len -= op;

							do {
								PUP(out) = PUP(from);
							} while(--op);

							from = out - dist;  /* rest from output */
						}
					} else if(write < op) {     /* wrap around window */
						from += wsize + write - op;
						op -= write;

						if(op < len) {          /* some from end of window */
							len -= op;

							do {
								PUP(out) = PUP(from);
							} while(--op);

							from = window - OFF;

							if(write < len) {   /* some from start of window */
								op = write;
								len -= op;

								do {
									PUP(out) = PUP(from);
								} while(--op);

								from = out - dist;      /* rest from output */
							}
						}
					} else {                    /* contiguous in window */
						from += write - op;

						if(op < len) {          /* some from window */
							len -= op;

							do {
								PUP(out) = PUP(from);
							} while(--op);

							from = out - dist;  /* rest from output */
						}
					}

					while(len > 2) {
						PUP(out) = PUP(from);
						PUP(out) = PUP(from);
						PUP(out) = PUP(from);
						len -= 3;
					}

					if(len) {
						PUP(out) = PUP(from);

						if(len > 1)
							PUP(out) = PUP(from);
					}
				} else {
					from = out - dist;          /* copy direct from output */

					do {                        /* minimum length is three */
						PUP(out) = PUP(from);
						PUP(out) = PUP(from);
						PUP(out) = PUP(from);
						len -= 3;
					} while(len > 2);

					if(len) {
						PUP(out) = PUP(from);

						if(len > 1)
							PUP(out) = PUP(from);
					}
				}
			} else if((op & 64) == 0) {         /* 2nd level distance code */
				this = dcode[this.val + (hold & ((1U << op) - 1))];
				goto dodist;
			} else {
				strm->msg = (char*)"invalid distance code";
				state->mode = BAD;
				break;
			}
		} else if((op & 64) == 0) {             /* 2nd level length code */
			this = lcode[this.val + (hold & ((1U << op) - 1))];
			goto dolen;
		} else if(op & 32) {                    /* end-of-block */
			Tracevv((stderr, "inflate:         end of block\n"));
			state->mode = TYPE;
			break;
		} else {
			strm->msg = (char*)"invalid literal/length code";
			state->mode = BAD;
			break;
		}
	} while(in < last && out < end);

	/* return unused bytes (on entry, bits < 8, so in won't go too far back) */
	len = bits >> 3;
	in -= len;
	bits -= len << 3;
	hold &= (1U << bits) - 1;

	/* update state and return */
	strm->next_in = in + OFF;
	strm->next_out = out + OFF;
	strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
	strm->avail_out = (unsigned)(out < end ?
	                             257 + (end - out) : 257 - (out - end));
	state->hold = hold;
	state->bits = bits;
	return;
}

/*
   inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
   - Using bit fields for code structure
   - Different op definition to avoid & for extra bits (do & for table bits)
   - Three separate decoding do-loops for direct, window, and write == 0
   - Special case for distance > 1 copies to do overlapped load and store copy
   - Explicit branch predictions (based on measured branch probabilities)
   - Deferring match copy and interspersed it with decoding subsequent codes
   - Swapping literal/length else
   - Swapping window/direct else
   - Larger unrolled copy loops (three is about right)
   - Moving len -= 3 statement into middle of loop
 */

#endif /* !ASMINF */
